Devices for the heating of sterile surgical liquids are known in the art. In a wide variety of surgical procedures, sterile fluids are used to irrigate the site of the surgery. It is important that the temperature of the fluids used be strictly controlled. As the portion of the brain that regulates body temperature is shut down with anesthesia, it is important that the introduction of sterile fluids does not cool the body core temperature. Clinical studies have indicated that a range of adverse consequences arise from a change in body core temperature of as few as one to three degrees Celsius. The adverse consequences from mild perioperative hypothermia include hypertension and increased vascular resistance, cardiac events, coagulopathy, an increase risk of surgical wound infections, and delays in the body's ability to remove drugs from its systems. Another specific adverse consequence is shivering which can increase metabolic rate up to 500% and thus increase demands for oxygen and the need to clear carbon dioxide. This list of complications is by no means exhaustive, but it illustrates the critical importance in controlling the body core temperature. Careful control of the temperature of sterile irrigation fluids is an important part of controlling body core temperature.
The prior art includes various devices for warming sterile fluid. Some are incorporated into a rolling cabinet for placement in a convenient place within the sterile field in an operating room so that sterile fluid is available at an appropriate temperature for use in the surgery such as irrigation or lavage.
One prior art solution is depicted in FIG. 1. Before describing the contents of FIG. 1 it is appropriate to note that FIG. 1 and the other figures that follow are adapted to facilitate a presentation of the teachings of the present invention. As such, the Figures are not intended to convey the precise relative dimensions of the various components. For example, surgical drapes are referenced in a number of figures and these drapes have been drawn with relatively thicknesses that are out of proportion so that the drape layer can be readily seen in the diagram.
Returning to FIG. 1, a cabinet 104 with an integrated and permanently attached metal basin (“integrated basin”) 108 provides a cavity for receipt of sterile fluids. In order to provide a separation between the sterile field and the reusable cabinet with integrated basin, a custom fit surgical drape 112 is laid on the cabinet and matches the cavity formed by the integrated basin. The sterile fluid 116 is placed in the drape.
A conventional heater 118 comprised of etched foil strips 120 in a slab 124 of silicon rubber is connected by an adhesive (not shown) to the underside of the integrated basin 108. A temperature measuring device 128 provides an input to controller 132 which turns on and off the power provided to heater 118. The controller 132 receives instructions from a user to increase or decrease the set point temperature for the heater 118 based on the user's desire to increase or decrease the temperature of the surgical fluid 116.
It is recognized as desirable that the heating process of the basin containing the fluids be capable of quickly heating fluid to bring it to the appropriate temperature. It is also recognized that having localized hot spots is undesirable as is using a heater that can apply so much heat that it can damage the surgical drape. Use of a heater that can expose personnel to heated surfaces that are hot enough to cause injury is undesirable and in some cases contrary to governmental regulations.
The integrity of the sterile field is important during surgery. Any breach that might indicate that the sterile field has become contaminated is taken very seriously. A breach that is undiscovered for a period of time is especially troublesome as it is difficult to assess when the breach was created and whether it caused the patient to be exposed to contaminants while vulnerable during surgery. Thus, it is no wonder that concerns from breaches in the sterile drapes 112 were taken very seriously. U.S. Pat. No. 6,910,485 for Medical Solution Thermal Treatment System and Method of Controlling System Operation in Accordance with Detection of Solution and Leaks in Surgical Drape Container addresses this concern Likewise, issued U.S. Pat. No. 6,091,058 for Thermal Treatment System and Method for Maintaining Integrity and Ensuring Sterility of Surgical Drapes Used with Surgical Equipment teaches ways of reducing the risk of damage to surgical drapes from objects placed in the drape covered basin.
Thus, problems associated with the recognized risk of a breach in a sterile drape have led others to develop various ways of reducing this risk or at least quickly detecting the breach.
In order to provide peace of mind to those working in the surgical theater, it would be advantageous to provide a way to use a disposable basin or a freestanding metal basin that could be sterilized.
Plastic basins are ubiquitous in hospitals and are used in many ways. Plastic basins that are sterilized (for example through irradiation or ethylene oxide gas sterilization) can safely be used in the sterile field without a surgical drape. In fact it is already extremely common to use a sterilized plastic basin in the sterile field to hold sterile fluids, so surgical room staff are confident that a plastic basin is sufficiently durable to handle the full range of abuse that can come from such use. Although recognized as durable, these simple unheated plastic basins cannot hold the sterile fluids above ambient temperature for an indefinite period of time.
An alternative to plastic basins is metal basins that are sterilized and safely reused just as a range of surgical implements are sterilized and reused.
The use of such basins would provide peace of mind as it is difficult to conceive of any activity in the sterile field that could cause a breach in a non-defective plastic or metal basin. A secondary benefit would be that standard gradation marks on the inside walls of the removable basin would provide a visual indication of the amount of sterile fluid remaining in the removable basin. As using basin gradation marks is done by hospital personnel in other contexts including short term holding of pre-heated sterile fluid in operating rooms, the use of fluid gradation marks in this context will seem familiar.
Using removable basin inside the sterile drape found in FIG. 1 is not without problems. Turning now to FIG. 2, a sterile removable basin 204 such as a sterile plastic basin has been placed on top of existing surgical drape 112. This provides the peace of mind from having a substantial removable basin 204 to contain the sterile fluid 116 without fears for the integrity of the surgical drape 112. The surgical drape 112 still has a role in isolating the liquid warming device cabinet 104 and the integrated basin 108 from the sterile field.
As in FIG. 1, a conventional heater 118 comprised of etched foil strips 120 in a slab 124 of silicon rubber is connected by an adhesive (not shown) to the underside of the integrated basin 108. A temperature measuring device 128 provides an input to controller 132 which turns on and off the power provided to heater 118. The controller 132 receives instructions from a user to increase or decrease the set point temperature for the heater 118 based on the user's desire to increase or decrease the temperature of the surgical fluid 116.
In order to examine the problems that would arise from the simple addition of a removable basin 204, it is necessary to examine what happens when it comes time to increase the temperature of sterile fluid 116. When the set point used by controller 132 exceeds the temperature measured at temperature measuring device 128 the heater 118 is turned on. As the slab 124 of silicon rubber has a non-zero specific heat, some of the heat from the heater goes to heat the slab 124 so the heated slab 124 can in turn increase the temperature of the bottom of the integrated basin 108 in the top of the liquid warmer device cabinet 104. The integrated basin 108 has its own non-zero specific heat and thus its own thermal mass which must be moved to a new higher temperature.
As the integrated basin 108 heats up, it passes some heat through the surgical drape 112 to the bottom of the removable basin 204. Unfortunately, the top of the integrated basin 108 and the bottom of the removable basin 204 do not mate perfectly so there are points of contact 136 with surgical drape 112 sandwiched between but also regions of air 140 which serve as insulators to slow the passage of heat from the top of the integrated basin 108 and the bottom of the removable basin 204. The air pockets 140 can be above or below the surgical drape 112. Points of contact work well for transferring heat; conversely, the presence of these air regions slows the transfer of heat and causes some spots on the removable basin 204 to be hotter than other spots.
The adjustment of the prior art solution as shown in FIG. 1 to use a substantial removable basin 204 is not optimal with respect to efficiently imparting heat to a basin and avoiding the creation of hot spots on the bottom of the basin. The magnitude of the problem is driven largely by the degree to which the bottoms of the removable basins are not flat or otherwise uniform. To a lesser extent, the problem is exacerbated by irregularities in the upper surface of the integrated basins 108.
An additional problem with this modification to the prior art is an aggregated thermal mass that is relatively high and there are a number of insulators, thus slowing any change in the temperature of the surface contacting the removable basin, drape, or other container. The thermal mass problem slows the response of the system both to increase heat and to decrease the heat.
FIGS. 3(A)-(C) shows the bottoms of three different removable basins that could be used as removable basin 204 in FIG. 2. The basins include protrusions outward (downward when the removable basin is positioned so that it can receive fluid) and indentations into the surface of the removable basin. Each basin bottom poses its own problems. The basin shown in FIG. 3(A) has three arc-shaped ridges that rise 0.054 inches outward. There are also two circular ridges with one located away from the center of the basin bottom.
FIG. 3(B) has a combination of another set of arc-shaped ridges but a different height and different radial distance from the center than those found in FIG. 3(A). A second complication is an indented region at the center of the basin bottom.
FIG. 3(C) poses yet another problem as the empty basin starts out with effectively only an outer ring that makes contact as there is a indentation of 0.025 inches for the majority of the bottom surface and an extra indentation of another 0.025 inches in a region at the center of the basin bottom.
There three examples are not exhaustive of all the irregularities found in removable basin bottoms, but they do illustrate the magnitudes and types of irregularities. One can appreciate that it would be difficult to design a corresponding set of irregularities into the surface of the integrated basin in order to promote surface to surface contact between basins (ignoring the surgical drape for a moment). Even if one could implement the appropriate set of reversed indentations and protrusions, the irregular symmetry around the center of the basin bottom would require alignment guides to help line up the various arcs or non-centered rings on the removable basin bottom with the corresponding portions of the integrated basin. The problem is greatly magnified if the goal is to be able to provide good surface to surface contact between the integrated basin and several different removable basin bottoms.